1. Field of the Invention
This invention relates in general to electrical circuits, and in particular to a full bridge converter current sense approach using virtual current summing and cancellation.
2. Description of Related Art
Semiconductor components typically operate using direct current supplied at a low, closely controlled voltage. Close regulation of unipolar voltage is required because nearly all semiconductor components operate best at a constant power supply voltage.
Switch mode power supplies are widely included among the most efficient of regulated power supplies because they provide fine voltage regulation while minimizing unusable power over a wide range of unregulated unipolar input voltages and output currents. A typical application for a switch mode power supply is to connect the switch mode power supply to an unregulated, high voltage direct current input source, and use switching elements, an output transformer, output rectifying and filtering components, and a feedback control circuit controlling the switching elements to provide regulated power to the desired circuit.
Typically, to control the power transferred through the output transformer, the "on time" of the switching elements used to apply the voltage generated by the direct current input source to the output transformer is varied. The feedback control circuit generates control signals that are used to control the duty cycle of the switching elements, typically in response to a direct or indirect measure of the power drawn from the output transformer. This measure is typically done by current sensing the current drawn from the output transformer, usually in an indirect manner.
As observed above, detection of power drawn from an output transformer may be direct or indirect. In the full bridge topology, determining the current in the primary winding of the output transformer is desirable for current mode control of the feedback control circuitry. The current in the primary winding reflects current in the secondary winding and thus is related to power demanded by the load connected to the rectifying and filtering circuitry.
A full bridge power supply and voltage regulator has four arms, two of which carry the current through the primary at any given time. No current is carried by a given arm in the bridge at least half the time. Current sensing is typically performed using a current sensing transformer, and is typically performed in one of the arms which allows for reset of the current sensing transformer during the zero current periods. Typical related art approaches place the current transformer in either one of the legs, or next to the transformer, to allow the current transformer to reset. However, placement of the current sensing transformer in one of the legs prevents sensing of "shoot through" currents in one or both of the arms of the full bridge supply.
It can be seen, then, that there is a need in the art for a full bridge power supply that can accurately sense the current delivered by the power supply. It can also be seen, then, that there is a need in the art for a full bridge power supply that can sense shoot through currents in both legs of the supply.